全文获取类型
收费全文 | 4331篇 |
免费 | 31篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 17篇 |
化学工业 | 249篇 |
金属工艺 | 51篇 |
机械仪表 | 36篇 |
建筑科学 | 126篇 |
矿业工程 | 7篇 |
能源动力 | 66篇 |
轻工业 | 204篇 |
水利工程 | 14篇 |
石油天然气 | 10篇 |
无线电 | 174篇 |
一般工业技术 | 372篇 |
冶金工业 | 2798篇 |
原子能技术 | 13篇 |
自动化技术 | 226篇 |
出版年
2022年 | 14篇 |
2021年 | 13篇 |
2019年 | 19篇 |
2018年 | 13篇 |
2017年 | 21篇 |
2015年 | 20篇 |
2014年 | 24篇 |
2013年 | 115篇 |
2012年 | 55篇 |
2011年 | 86篇 |
2010年 | 70篇 |
2009年 | 59篇 |
2008年 | 71篇 |
2007年 | 78篇 |
2006年 | 68篇 |
2005年 | 71篇 |
2004年 | 62篇 |
2003年 | 63篇 |
2002年 | 43篇 |
2001年 | 49篇 |
2000年 | 47篇 |
1999年 | 109篇 |
1998年 | 836篇 |
1997年 | 480篇 |
1996年 | 298篇 |
1995年 | 223篇 |
1994年 | 183篇 |
1993年 | 198篇 |
1992年 | 57篇 |
1991年 | 55篇 |
1990年 | 49篇 |
1989年 | 50篇 |
1988年 | 46篇 |
1987年 | 43篇 |
1986年 | 45篇 |
1985年 | 47篇 |
1984年 | 22篇 |
1983年 | 16篇 |
1982年 | 34篇 |
1981年 | 38篇 |
1980年 | 38篇 |
1979年 | 24篇 |
1978年 | 28篇 |
1977年 | 82篇 |
1976年 | 142篇 |
1975年 | 17篇 |
1974年 | 13篇 |
1973年 | 19篇 |
1972年 | 14篇 |
1968年 | 13篇 |
排序方式: 共有4363条查询结果,搜索用时 15 毫秒
31.
32.
33.
H.W. Choi C.W. Jeon M.D. Dawson P.R. Edwards R.W. Martin 《Photonics Technology Letters, IEEE》2003,15(4):510-512
High-performance, two-dimensional arrays of parallel-addressed InGaN blue micro-light-emitting diodes (LEDs) with individual element diameters of 8, 12, and 20 /spl mu/m, respectively, and overall dimensions 490 /spl times/490 /spl mu/m, have been fabricated. In order to overcome the difficulty of interconnecting multiple device elements with sufficient step-height coverage for contact metallization, a novel scheme involving the etching of sloped-sidewalls has been developed. The devices have current-voltage (I-V) characteristics approaching those of broad-area reference LEDs fabricated from the same wafer, and give comparable (3-mW) light output in the forward direction to the reference LEDs, despite much lower active area. The external efficiencies of the micro-LED arrays improve as the dimensions of the individual elements are scaled down. This is attributed to scattering at the etched sidewalls of in-plane propagating photons into the forward direction. 相似文献
34.
Radkovskaya A. Sydoruk O. Shamonin M. Shamonina E. Stevens C.J. Faulkner G. Edwards D.J. Solymar L. 《Microwaves, Antennas & Propagation, IET》2007,1(1):80-83
Magnetoinductive waves propagating along a line consisting of two kinds of metamaterial elements are studied. Both elements are made up by the same metallic loop but are loaded by different capacitors resulting in different resonant frequencies. The dispersion characteristics are derived from phase and amplitude measurements for the cases when the line consists of (i) identical elements and (ii) of alternating elements. Both planar (elements in the same plane as the axis of the line) and axial (elements perpendicular to the axis of the line) configurations are investigated. It is shown that in the bi-periodic arrangement of the elements, the dispersion curves have a forward wave in the lower frequency branch and a backward wave in the upper frequency branch independent of the configuration whether it is planar or axial. Comparisons between theoretical and experimental results show good agreement 相似文献
35.
CD Holyoak M Stratford Z McMullin MB Cole K Crimmins AJ Brown PJ Coote 《Canadian Metallurgical Quarterly》1996,62(9):3158-3164
The weak acid sorbic acid transiently inhibited the growth of Saccharomyces cerevisiae in media at low pH. During a lag period, the length of which depended on the severity of this weak-acid stress, yeast cells appeared to adapt to this stress, eventually recovering and growing normally. This adaptation to weak-acid stress was not due to metabolism and removal of the sorbic acid. A pma1-205 mutant, with about half the normal membrane H+-ATPase activity, was shown to be more sensitive to sorbic acid than its parent. Sorbic acid appeared to stimulate plasma membrane H+-ATPase activity in both PMA1 and pma1-205. Consistent with this, cellular ATP levels showed drastic reductions, the extent of which depended on the severity of weak-acid stress. The weak acid did not appear to affect the synthesis of ATP because CO2 production and O2 consumption were not affected significantly in PMA1 and pma1-205 cells. However, a glycolytic mutant, with about one-third the normal pyruvate kinase and phosphofructokinase activity and hence a reduced capacity to generate ATP, was more sensitive to sorbic acid than its isogenic parent. These data are consistent with the idea that adaptation by yeast cells to sorbic acid is dependent on (i) the restoration of internal pH via the export of protons by the membrane H+-ATPase in an energy-demanding process and (ii) the generation of sufficient ATP to drive this process and still allow growth. 相似文献
36.
37.
O Castillo de Febres MD Decker M Estopinan G Bordones KM Edwards 《Canadian Metallurgical Quarterly》1994,13(7):635-639
The safety and immunogenicity of primary immunization at 2, 4 and 6 months of age with Haemophilus influenzae type b capsular polysaccharide conjugated to tetanus toxoid (PRP-T; Act-HIB) were evaluated in infants in Valencia, Venezuela. In order better to assess reactions to PRP-T, subjects received their initial PRP-T vaccine a mean of 6.5 days after their initial diphtheria-tetanus-pertussis (DTP) vaccine. The PRP-T vaccine was well tolerated. Serum was obtained at ages 2 and 7 months (before the first and 1 month after the third PRP-T dose). Antibody responses were compared with those from Nashville infants who had received PRP-T and DTP simultaneously in a previous trial. The preimmunization titers in the Venezuelan and Nashville infants did not differ. The geometric mean postimmunization titer in the Venezuelan infants was 37.9 micrograms/ml, as compared with 3.63 micrograms/ml in the Nashville infants (P < 0.00001). Possible explanations for the exceptional antibody response of these Venezuelan infants to PRP-T include carrier priming caused by prior DTP immunization, synergy associated with the specific DTP vaccine used, preimmunization immunologic experience that differed from their United States counterparts and genetic differences that altered response to the vaccines. Further studies are proposed to evaluate these possibilities. 相似文献
38.
F Deák á Horváth á Kiss Z Seres A Galonsky CK Gelbke H Hama L Heilbronn D Krofcheck WG Lynch DW Sackett HR Schelin MB Tsang J Kasagi T Murakami 《Canadian Metallurgical Quarterly》1995,52(1):219-227
An extruding wire knife was used to give adult male CFHB rats a minimally traumatic unilateral mechanical lesion of the medial forebrain bundle. In addition, some rats received bilateral intrastriatal injections of one of three fluorescent retrograde tracers either eight days before or eight days after the lesion. Injections made after the lesion revealed that about half of the animals had complete lesions of the nigrostriatal tract, while the other half were incompletely lesioned, the mean proportion of non-axotomized neurons being 23%. Over the 10 weeks following the lesions, the number of tyrosine hydroxylase-immunoreactive cells in the lesioned substantia nigra fell linearly, reaching a mean of 29% of that of the control substantia nigra. In the animals which were completely lesioned, neuronal survival at 10 weeks varied between 6 and 12%. That the disappearance of tyrosine hydroxylase-immunoreactive neurons was due to cell death rather than the loss of tyrosine hydroxylase itself was confirmed by labelling the cells with Fluoro Gold before axotomy; the tracer was seen in survival neurons, microglia and in a few involuted neurons which continued to be tyrosine hydroxylase-immunoreactive. This percentage of neurons surviving axotomy corresponds to the proportion of substantia nigra neurons which project to the contralateral striatum, and these neurons were in the region of the substantia nigra from which the contralateral projection originated. It is concluded that following mechanical transection of the nigrostriatal tract, all truly axotomized substantia nigra neurons die over a period of about 10 weeks. 相似文献
39.
Selenium is essential for humans because it protects the heart against cardiomyopathy. It may also reduce ischaemic heart disease owing to its antioxidant activity. It is known that Indian migrants in a number of countries have high incidences of ischaemic heart disease. In this study, fasting plasma selenium concentrations of Sikh migrants in Sydney (Australia) were measured to investigate whether selenium concentration is reduced in this community. The mean concentration of selenium in plasma (91.8 +/- 15.0 ng ml-1, n = 196) was within the normal range. A significantly higher plasma selenium concentration was demonstrated in males than in females (p < 0.01). This was mainly due to the difference in mean selenium concentrations between genders in vegetarians because no significant difference was observed in non-vegetarian males versus females. The mean concentration of selenium in teetotal males was similar to those who consumed alcohol. Despite significant variations with gender and diet, the selenium concentrations were within the normal range. The results suggest that selenium status is adequate in the Sikh community even though vegetarian diet is common and alcohol use is condones in males. 相似文献
40.
JP Binette MB Binette MA Gawinowicz N Kendrick 《Canadian Metallurgical Quarterly》1996,10(2):509-17; discussion 517-8
The discovery of an organic component in kidney stones dates back to 1684. More than 150 years elapsed before the incrustation of this organic component, which is now called the matrix, was proposed as the mechanism of stone formation. The composition of the matrix remained largely unknown until the development of electron microscopy and the advances in biochemistry combined in the 1950's to usher in the modern era of renal stone matrix investigation. Composed mainly of selectively incorporated proteins generally characterized by high glutamic and aspartic acid content and the frequent occurrence of gamma-carboxyglutamic acid, the matrix displays a variable and complex composition and shares a few proteins in many stones. The embryonic stone may first appear in the renal tubules where it can acquire the blood and cell membrane proteins recently found by analysis of stone protein extracts. The combination of supersaturation, an appropriate environment, the availability of calcium binding proteins which may be abnormal, and the incorporation of proteins extracted from leukocytes and cell wall membranes may induce stone formation. 相似文献